Yuriy
OK Upon closer look at your demo-video, I see what you are saying.
However I am not sure I agree about something.
Given a trace, without an underlying plane, as the frequency increases,
the current density is higher around the surfaces (top, bottom and
sides) than it is in the middle of the trace. Absent any external
influence, the current density decays exponentially from a surface to
the centerline of the trace. In general, the current density pattern
would be symmetrical around the trace (top to bottom, side to side).
Now, bring a plane adjacent to the trace. This introduces an effect
typically called a proximity or a ground effect. The opposite sign
attraction causes some of the current flowing on the top (far) surface
to migrate to the bottom (close) surface. So the current density shifts
a little --- higher on the bottom surface, not as high on the top
surface, but still smallest along the middle or centerline of the trace.
The mutual inductance effect that causes the skin effect in the first
place dominates the opposite sign attraction of the proximity effect, so
the current is still smallest at the centerline.
All of this is true, at any frequency.
It seems to me your simulation at around 2:45 starts to support that, on
both the trace and the plane.
Do you agree with me so far?
If so, why is it that "current density is not lower in the middle of the
plane."
Doug
Yuriy Shlepnev wrote:
Hi Doug,
The current density is not lower in the middle of the plane - it is just
visual impression. Smaller number of arrows is used in the middle of the
metal layer and it may create impression that the density values are lower in
the middle (same for power flow densities). Each arrow and color presents the
Current Density value in A/m^2 at a particular location within the metal.
Density of the arrows does not correlate with the current density (see more
at webinar #7 at https://www.simberian.com/Webinars.php).
The value of the current density is actually lower on the opposite side of
planes and gradually decreases from one side to another - it is obvious on
the color or blanket plots shown at
https://www.simberian.com/AppNotes/PlaneCurrentDensity.gif
It would be different if trace is at the edge of the plane or near a cut-out
in the plane. You will see current higher at the edges and on the opposite
side of the plane - I think I visualized it at some demos.
Best regards,
Yuriy
-----Original Message-----
From: Doug Brooks [mailto:dbrooks9@xxxxxxxxxxxxxxx]
Sent: Sunday, December 8, 2019 12:59 PM
To: shlepnev@xxxxxxxxxxxxx; 'SI'
Subject: Re: [SI-LIST] Skin effect on ground plane?
Hi Yuriy
Your simulation is exactly what I was looking for. But I have one question.
You show that at moderate frequencies there is current density on both
the top and bottom surfaces of the plane, with a lower current density
down the centerline of the plane. But at very high frequencies the
current density only exists on the top surface of the plane (closest to
the trace) with effectively no current density on the bottom surface.
What causes the difference in the two conditions, and why?
Thanks
Doug
Yuriy Shlepnev wrote:
Hi Doug,
Yes, there is proximity as well as skin effects on the planes - the area
where signal power flow is shrinking with the frequency and current flowing
in thinner and thinner surface layer (result of absorption by the metal).
And all signal power is in dielectric and air! :)
See illustrations for microstrips at
https://www.simberian.com/ScreenCasts.php?id=38 and in some other ;
demo-videos at https://www.simberian.com/ScreenCasts.php?view=table or at ;
Simbeor channel at https://www.youtube.com/user/simbeor/videos
Best regards,
Yuriy
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Doug Brooks
Sent: Friday, December 6, 2019 10:32 AM
To: SI
Subject: [SI-LIST] Skin effect on ground plane?
We all know what the skin effect is on a trace. And we all know the
return signal path is on the plane directly under the trace.
The question is, is there a corresponding skin effect on the ground plane?
Doug Brooks
